The present invention relates to a vane type fluid machine, and particularly to an improvement in a vane type fluid machine having a casing, a rotor rotating in the casing, and a plurality of vanes supported by the rotor to slide on an inner surface of the casing.
The applicant has suggested a fluid machine of this type in which a rotor chamber substantially in the form of an athletic track in a phantom plane including a rotation axis of a rotor is provided in a two-divided casing, and a substantially U-shaped seal portion of each vane slides on an inner surface of the rotor chamber (see the specification and drawings of Japanese Patent Application No. 11-57933).
In this case, when a minute recess and projection or a minute step due to a deviation between mating surfaces of the casing exists on the inner surface of the rotor chamber, sealing performance between the inner surface of the rotor chamber and the seal portion is impaired since the seal portion is made of hard PTFE (polytetrafluoroethylene) and cannot be deformed to fit the minute recess and projection or the like.
Thus, the inner surface of the rotor chamber must be micromachined, but the rotor chamber has a specific shape as described above, and therefore, a long time is required for its micromachining, thereby causing an increase in cost of the fluid machine.
The present invention has an object to provide a vane type fluid machine in which an improved structure of a seal portion of each vane can secure good sealing performance even if machining accuracy of an inner surface of a casing is alleviated.
To achieve the first object, according to the present invention, there is provided a vane type fluid machine including: a casing; a rotor rotating in the casing; and a plurality of vanes supported by the rotor to slide on an inner surface of the casing, wherein a seal portion of each vane is formed to be elastically deformable so as to slide on the inner surface of the casing with the seal portion bent backward of a rotational direction of the rotor.
Forming the seal portion of each vane as described above allows the seal portion to be elastically deformed to fit shapes of a minute recess and projection or a minute step, even if they exist on the inner surface of the casing, so that sealing performance between the seal portion and the inner surface of the casing can be secured to allow alleviation in machining accuracy of the inner surface of the casing.
When a surface pressure of the seal portion is increased by a centrifugal force accompanying high speed rotation of the rotor, a heating value due to sliding is increased to impair durability of the seal portion. Such occurrence of defects are automatically avoided by actions mentioned below. Specifically, during high speed rotation of the rotor, a kinetic pressure in a wedge-shaped space formed between a front surface of the seal portion in a rotational direction of the rotor and the inner surface of the casing is increased, and the kinetic pressure is further increased by an increased amount of deformation of the seal portion by the centrifugal force. The increased kinetic pressure becomes a pressing force of the seal portion on the inner surface of the casing, and a pressure acting on a tip of the seal portion is reduced since a point of application of the pressing force is displaced closer to a base rather than the tip of the seal portion by deformation thereof. This restrains an increase in the surface pressure of the seal portion, and reduces the heating value due to sliding to significantly improve durability of the seal portion. When a value of the kinetic pressure in the wedge-shaped space is higher than a design value, the seal portion is significantly deformed to release an excess of the kinetic pressure, thereby keeping the kinetic pressure in the wedge-shaped space substantially constant.